In the construction of roads and related projects, the amount of documentation and data which are factors in creating a model of the project is considerable. In addition, there exists a huge variety of data sets including paper plans and printed specification books that define how a road is to be constructed, Computer Aided Design (CAD) files of these same drawings, as well as a wide variety of software and data storage formats used in the design of the roads.
The process of transferring designs into road models and road models into formats that are readily usable by field devices is cumbersome in the current art. When a single road model is interpreted by different field devices it will lead to different interpretations and results. Early road modeling software lacked the ability to explicitly describe a road and all its components like the intersections. Interpretation of road models generated by these early road modeling packages could vary considerably but be technically acceptable based upon the information provided in the model. The most common methodology uses alignments and templates of cross sections along the alignments to describe a road. Road modeling software that attempts to apply one template from those alignments will have trouble modeling a divided highway with multiple roadways and ramps joining and leaving the roadways. When a single element changes, the entire template typically has to be redefined. This typically results in numerous revisions to the model being sent to the field. Also, if a road model is constrained by the limitations of a given file format, the result can be so complex that it is difficult to verify whether the road is correct, to find errors in the road, or to even understand the model. This is particularly difficult in the field where interaction with the designers may be difficult.
Additionally, the numerous file formats define elements of the road model in different manners. For example, the way one template transitions to another template is different in various road model field formats. This means that elements of the original road model will convert differently to each of the field file formats. Thus, different field devices may interpret the same road model differently even though they are reading from the same file, potentially leading to different models of the same road.
FIG. 1 shows an exemplary representation of a conventional road model. In FIG. 1, a roadway 101 is shown with a center line 105. Spaced along center line 105 is a series of cross sections (e.g., 106a, 106b, 106c, 106d, 106e, 106f). The cross sections show the profile of the road section at that particular portion of roadway 101. Cross section 106c is shown in greater detail in FIG. 1. The elevations associated with a particular cross section may be defined as an actual elevation of portions 110, 111, and 112 of cross section 106c, or by any relative reference from another defined elevation. Contractors rely on the field software to interpolate elevations of the road model between cross-sections to create a continuous road surface. Thus, two devices, reading the same model in the field, could calculate different elevations for the same point.
One problem associated with using cross section road models is that they are not well suited for representing the road surface at an intersection. FIG. 2 shows an exemplary representation of a conventional road model of an intersection. In FIG. 2, roadway 101 is intersected by roadways 201 and 202. Roadways 201 and 202 each have a corresponding center line 205 and 210 associated therewith. Also shown is a center line 215 of a turn lane from roadway 101 to roadway 202. For clarity the spacing of the cross sections shown in FIG. 2 is greater than would typically be used with an intersection as represented in FIG. 2. This is because, in actual road models, curves and other complex shapes require closer spacing of the cross sections compared with straight sections of roadway in order to accurately represent the shape of the roadway. In FIG. 2 the plurality of cross sections where roadways meet creates an excessive number of cross sections in the road model. This makes it difficult for the creator of the road model to verify with absolute certainty that the road model is indeed correct. This also leads to the field device incorrectly interpreting the road model.
FIG. 3 shows an exemplary representation of another conventional road model. In FIG. 3 a roadway 301 is defined by strings 302 and 303 and a center line string 304. In the field, a contractor may lay out an actual string at the location and elevation of points of the road model string. It is appreciated that a particular road model may typically use a different number of strings than shown in FIG. 3. Strings 302, 303, and 304 are geometries which run parallel with roadway 301 and describe the geometry of roadway 301. A given point along a string (e.g., string 302) can be described with a 2-dimensional location and an associated elevation (e.g., station/offset/cross slope). Again, the elevation may be described using the actual elevation at that point, or as an offset from another elevation.
Strings are advantageous over cross section road models in that at road intersections, there are fewer intersecting data points which makes it easier to interpret and verify by the contractor. In a road model using strings, each layer of the roadway is defined by a separate set of strings. Thus, the top surface of a road is defined by one set of strings, and the top surface of any sublayer is separately defined by respective sets of strings. As a result, at an intersection, the road model comprises numerous layers of strings which cross each other. It is unusual for layers of different roads to match even though the implication in the design is that common layers should match. This would result in gaps, bumps, or drainage problems at the intersection if the intersection were built following the model.
In the past, slight differences in the elevation of road layers would be smoothed by the operator of the road construction equipment. However, machine control systems are increasingly being used in the road construction industry. The machine control systems access a data file and can control the location, angle, and elevation of an implement (e.g., a blade of a bulldozer or grader) to precisely match the road model. In straight sections of roads, machine control systems are well suited for constructing the road according to the model. However, machine control systems do not allow an operator to “eyeball” a smooth transition between the roadway surfaces at an intersection.
Additionally, cross-section and string based road modeling systems have difficulties in matching the layers in a manner which is convenient to the user.